The present invention relates generally to a system and method for controlling the idling speed of an automotive internal combustion engine. More specifically, the invention relates to an idling speed adjustment depending upon the required cooling efficiency of an automotive air conditioning system.
In conventional engine idling control systems, idling speed is derived predominantly on the basis of engine or engine coolant temperature. Various correction parameters have been employed to control the engine idling speed more precisely corresponding to engine conditions. Among such known engine idling speed correction parameters, so-called "idle-up" is performed in response to operation of an automotive air conditioning system in air-conditioning (A/C) mode. In the "idle-up" operation, the engine idling speed is increased by a predetermined value. Conventionally, the increment to the engine idling speed in "idle-up" operation has been a fixed value selected so as to obtain maximum efficiency of a cooled air source, such as an evaporator, in the air conditioning system.
On the other hand, the required cooling efficiency of the air conditioning system varies substantially with envirounmental conditions of the vehicle, such as atmospheric temperature, humidity, vehicle cabin temperature, desired cabin temperature and so forth. Therefore, it will be appreciated that the maximum cooled air source efficiency is not always required for satisfactory air conditioning and dehumidification. This, in turn, means that the engine idling speed need not necessarily be increased to the fixed speed to achieve maximum efficiency of the cooled air source of the air conditioning system, depending upon environmental conditions.